This invention relates generally to apparatus for separating particles from dirty liquid and more particularly to a magnetic separator of the type commonly used to clean machine tool coolant by magnetically removing entrained metal particles from the coolant.
In such a separator, dirty liquid is delivered to a flow path defined in part by a curved apron extending around the lower side of a rotatable drum, the drum having a generally magnetic outer shell. As the liquid flows to and around the drum, the particles are magnetically attracted to the drum and thus are removed from the liquid. The drum is slowly rotated to raise the collected particles out of the flow path and to enable the particles to be scraped from the drum and subsequently disposed of in a waste container.
The scraper has an inclined blade which is located in the magnetic field of the drum and which is disposed in contact with the outer shell of the drum at a position tending to create a dam causing coolant in the collected particles to drain back into the flow path and reduce the quantity of coolant carried to the waste container. A pushing force caused by particles subsequently delivered to the scraper by the rotating drum squeezes additional coolant from the buildup of particles at the inclined blade. Under most conditions, the pushing force from the subsequently delivered particles is sufficient to force the buildup of particles up the inclined scraper blade, through the magnetic field and toward a discharge chute. However, when the coolant is, for example, a heavy bodied oil, when the intrinsic magnetic attraction of the parties to the drum is low, or when the collected particles contain a large percentage of non-magnetic material, the pushing force is diminished and is insufficient to move the buildup of particles through the magnetic field which acts on the scraper blade. Under these conditions, some of the collected particles fall back into the flow path thereby reducing the efficiency of the separator.